On Mon, Feb 02, 2026 at 02:50:28AM -0500, Michael S. Tsirkin wrote: > On Sun, Feb 01, 2026 at 05:24:03PM -0800, Pierrick Bouvier wrote: > > On 1/31/26 9:48 AM, Michael S. Tsirkin wrote: > > > On Fri, Jan 30, 2026 at 06:00:56PM -0800, Pierrick Bouvier wrote: > > > > Signed-off-by: Pierrick Bouvier <[email protected]> > > > > > > Performance impact? > > > > > > the reason we have these is for performance ... > > > > > > > I would be very happy to run any benchmark that you might judge critical. > > > > Should we run a disk read/write sequence with a virtio disk, or a download > > with a virtio interface? Any other idea? > > block for sure, people who care about network perf go the vhost or > vhost user path. > > So I CC'd Stefan Hajnoczi. Stefan do you feel this needs a test and what > kind of test do you suggest as the most representative of I/O overhead?
This command-line lets you benchmark virtio-blk without actual I/O
slowing down the request processing:
qemu-system-x86_64 \
-M accel=kvm \
-cpu host \
-m 4G \
--blockdev
file,node-name=drive0,filename=boot.img,cache.direct=on,aio=native \
--blockdev null-co,node-name=drive1,size=$((10 * 1024 * 1024 * 1024)) \
--object iothread,id=iothread0 \
--device virtio-blk-pci,drive=drive0,iothread=iothread0 \
--device virtio-blk-pci,drive=drive1,iothread=iothread0
Here is a fio command-line for 4 KiB random reads:
fio \
--ioengine=libaio \
--direct=1 \
--runtime=30 \
--ramp_time=10 \
--rw=randread \
--bs=4k \
--iodepth=128 \
--filename=/dev/vdb \
--name=randread
This is just a single vCPU, but it should be enough to see if there is
any difference in I/O Operations Per Second (IOPS) or efficiency
(IOPS/CPU utilization).
Stefan
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